Ecologie bacterienne dans les bacs d'elevage larvaire de coquilles Saint-Jacques (Pecten maximus )

Larval rearings were performed with seawater either freshly pumped or after storage in a pond. Concerning bacterial populations these waters were characterized by a high diversity, little sized bacteria whose few of them (1%) were cultivable on Zobell medium. In the tanks, the bacterial ecosystem was modified by the presence of antibiotics, larvae and algae: the diversity was lowered, the cellular volume was increased by a factor 2 to 5, 100% bacteria were cultivable and chloramphenicol resistant, and their metabolism changed. Taxonomic screening showed no differences among the two waters neither at the beginning nor at the end of the rearings. However, depending on the water (stored or not) differences were identified for bacterial physiology and productivity: bacteria from the pond were more organic matter dependent. From these results we have developed a mathematical model which takes into account the influence of the respective productivity of both waters, the initial bacterial concentration, the organic matter content (seawater content and larval excretion) and the bacterial grazing by the larvae.